Surface smoothing of stereolithographically formed 3-D objects

Abstract

A stereolithographic method and apparatus for forming polymeric structures comprising a plurality of overlying layers, each layer formed by polymerizing a thin layer of liquid photopolymer on a prior layer. Crevices formed at the layer interfaces are filled by a stereolithographic method comprising lifting the multilayered structure from the liquid photopolymer, draining excess liquid therefrom, tilting the structure to provide an acute angle of incidence between an incident radiation beam and a side wall of the object, and applying radiation to the crevice to polymerize at least the surface of a quantity of liquid photopolymer therein. The structure may then be subjected to a separate final full cure to fully harden the structure. An exemplary use is the packaging of electronic components and the like.

What is claimed is:  
     
       1. A method of forming a smooth enclosure about lateral sides of a rectangular object, comprising: providing a rectangular object to be enclosed; forming sidewalls about lateral sides of said rectangular object as at least two superimposed, 
       contiguous layers of at least semisolid polymeric material defining at least one exposed  
       crevice therebetween containing liquid polymeric material remaining from the formation  
       of said layers; and  
       at least partially polymerizing said liquid polymeric material in said at least one exposed crevice.  
     
     
       2. The method of  claim 1 , wherein said providing said rectangular object comprises providing a semiconductor die. 
     
     
       3. The method of  claim 4 , further comprising covering at least one of a top and a bottom of said semiconductor die with said at least semisolid polymeric material. 
     
     
       4. The method of  claim 1 , further comprising providing a platform configured for positioning of said rectangular object thereon. 
     
     
       5. The method of  claim 1 , wherein said forming said sidewalls about said lateral sides of said rectangular object comprises: 
       submerging said rectangular object in a liquid photopolymer material to a first depth over an upper surface of said rectangular object;  
       applying a beam of polymerization stimulating radiation to selected regions of said liquid photopolymer material over said upper surface of said rectangular object to at least partially polymerize said liquid photopolymer material overlying said selected regions and form a first of said at least two superimposed, contiguous layers of at least semisolid polymeric material defining at least a portion of a sidewall, said first layer extending substantially parallel to said upper surface of said rectangular object;  
       submerging said rectangular object in said liquid photopolymer material to a second depth over said first layer;  
       applying a beam of polymerization stimulating radiation to selected regions of said liquid photopolymer material over said first layer to partially polymerize said liquid photopolymer material in said selected regions to form a second layer of at least semisolid photopolymer defining at least another portion of said sidewall, said second layer extending substantially parallel to said first layer, wherein said at least one exposed crevice is defined between at least one side of said second layer and said first layer and said at least one exposed crevice contains unpolymerized liquid photopolymer material.  
     
     
       6. The method of  claim 5 , further comprising generating said polymerization stimulating radiation beams as laser beams. 
     
     
       7. The method of  claim 5 , further comprising reorienting said rectangular object prior to at least partially polymerizing said liquid polymeric material in said at least one exposed crevice. 
     
     
       8. The method of  claim 5 , further comprising generating said polymerization stimulating radiation as ultraviolet radiation. 
     
     
       9. A method of forming a smooth enclosure about lateral sides of a rectangular object, comprising: 
       providing a rectangular object to be enclosed;  
       forming sidewalls about lateral sides of said rectangular object as at least two superimposed, contiguous layers of at least semisolid polymeric material wherein forming said at least two superimposed, contiguous layers comprises at least partially polymerizing a photopolymer using a moving beam of radiation, defining at least one exposed crevice therebetween containing liquid polymeric material; and  
       at least partially polymerizing said liquid polymeric material in said at least one exposed crevice.  
     
     
       10. The method of  claim 9 , wherein said liquid polymeric material in said at least one exposed crevice comprises a photopolymer and said at least partially polymerizing said liquid polymeric material in said at least one exposed crevice comprises traversing a beam of radiation along said at least one exposed crevice. 
     
     
       11. A method of forming a smooth enclosure about lateral sides of a rectangular object, comprising: 
       providing a rectangular object to be enclosed;  
       forming sidewalls about lateral sides of said rectangular object as at least two superimposed, contiguous layers of at least semisolid polymeric material defining at least one exposed crevice therebetween containing liquid polymeric material;  
       at least partially polymerizing said liquid polymeric material in said at least one exposed crevice; and  
       providing a platform configured for positioning of said rectangular object thereon, reorienting said platform about a horizontal axis thereof, said platform having said rectangular object thereon including said sidewalls formed about said lateral sides thereof.  
     
     
       12. A method of forming a smooth enclosure about lateral sides of a rectangular object, comprising: 
       providing a rectangular object to be enclosed;  
       forming sidewalls about lateral sides of said rectangular object as at least two superimposed, contiguous layers of at least semisolid polymeric material defining at least one exposed crevice therebetween containing liquid polymeric material, said forming said sidewalls about said lateral sides of said rectangular object comprises:  
       submerging said rectangular object in a liquid photopolymer material to a first depth over an upper surface of said rectangular object,  
       applying a beam of polymerization stimulating radiation to selected regions of said liquid photopolymer material over said upper surface of said rectangular object to at least partially polymerize said liquid photopolymer material overlying said selected regions and form a first of said at least two superimposed, contiguous layers of at least semisolid polymeric material defining at least a portion of a sidewall, said first layer extending substantially parallel to said upper surface of said rectangular object,  
       submerging said rectangular object in said liquid photopolymer material to a second depth over said first layer,  
       applying a beam of polymerization stimulating radiation to selected regions of said liquid photopolymer material over said first layer to partially polymerize said liquid photopolymer material in said selected regions to form a second layer of at least semisolid photopolymer defining at least another portion of said sidewall, said second layer extending substantially parallel to said first layer, wherein said at least one exposed crevice is defined between at least one side of said second layer and said first layer and said at least one exposed crevice contains unpolymerized liquid photopolymer material, and  
       at least partially polymerizing said liquid polymeric material in said at least one exposed crevice, said at least partially polymerizing said liquid polymeric material in said at least one exposed crevice comprises:  
       removing said rectangular object from said liquid photopolymer material, leaving a quantity of said liquid photopolymer material in said at least one exposed crevice,  
       orienting said rectangular object to permit access to said quantity of said liquid photopolymer material by said polymerization stimulating radiation beam, and  
       exposing said quantity of said liquid photopolymer material to polymerization stimulating radiation to at least partially polymerize at least an outer portion of said quantity of said liquid photopolymer material.  
     
     
       13. The method of  claim 12 , wherein said exposing said quantity of said liquid photopolymer material to said polymerization stimulating radiation comprises traversing said beam of polymerization stimulating radiation along said at least one exposed crevice.